EDIT:
All solved with vsprintf. Good old vsprintf. Also freed about 6 bytes of memory!

New post:

Hey people! I got a new version out today.
It can decompile codes for the slot-machine much better now, with commands for altering and checking the coin case, and some purely semantic commands (to prevent false data being decompiled).
The unknown commands are prefixed with a "CMD_" both in the program AND in the decompiled code, and are useless until I find out what they actually do :D
@swampert22: This version can now do that!